Our primary premise is that the proteins that make up the skeletal muscle calcium release unit (CRU i.e. SR/surface membrane or t-tubule couplings) interact with one another and that each of these proteins is needed to allow normal excitation contraction (EC) coupling to occur. Data from our dysgenic (mdg) mouse model have defined the critical regions of the slow voltage gated Ca 2+ channel in the surface membrane (alpha1s-DHPR) needed for bi-directional signaling with RyR1. Data from our dyspedic mouse model have shown that the SR Ca 2+ release channel (RyR1) is needed for the proper organization and function of the DHPR and studies undertaken to determine which portions of RyR1 are required to provide retrograde signaling with the DHPR have shown that they are discontinuous. New mouse models have been created that will allow us to study both proteins, in tandem, in a null background for both. Other mouse models have been or will be created to allow us to study the roles of triadin, junctin and junctate. We will also examine the roles of two accessory proteins homer, and calmodulin in the control of EC coupling. The themes of Projects 1-4 are closely interrelated, and the expertise from each is essential to the interdisciplinary goals of the proposed program. The administrative and tissue culture transgenic animal cores will provide a unifying resource and common reagents for all of the investigators. The scope of investigations will range from structure function analysis of the RyR1 and creation of null mice (Project 1), studies of isolated protein function after creation and expression of mutant and chimeric triadic proteins (Project 4), the effects of these changes on the lectrophysiology of the cells (Project 3), alterations of both resting and activated intracellular calcium (Project 1 and4), to morphologic correlates of these changes on the formation and maintenance of the triad and the proteins in the triad (Project 2).